Retirement-Related Benefits - Contributions (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Retirement-Related Benefits
Employer contributions	$ 317	$ 392
U.S. and Non-U.S. nonpension postretirement benefit plans
Retirement-Related Benefits
Employer contributions	269	265
Non-U.S. DB plans and multi-employer plans
Retirement-Related Benefits
Employer contributions	48	127
Pension Plans, Including Multi-employer Plans
Retirement-Related Benefits
Contributions by employer - Noncash	311	160
Nonpension Postretirement Plans | Non-U.S. DB plans
Retirement-Related Benefits
Contributions by employer - Noncash	$ 307	$ 315